The present invention relates to a method for the synthetic preparation of cyclopentyl trichlorosilane or, more particularly, to a method for the preparation of cyclopentyl trichlorosilane from trichlorosilane and cyclopentene by the hydrosilation reaction.
Cyclopentyl trichlorosilane is a compound having usefulness as an intermediate in the synthetic preparation of various kinds of organosilicon compounds having two or three cycloalkyl groups in a molecule. Since cyclopentyl-containing organosilicon compounds have a refractive index intermediate between those of methyl- and phenyl-containing organosilicon compounds, an advantage is expected in matching of the refractive indices when a transparent silicon composition is desired. Further, the bulkiness of the cyclopentyl group promisingly indicates the usefulness of cyclopentyl-containing silane compounds as a silylating agent in various organic synthesis for which tert-butyl dimethyl chlorosilane is the most conventional. Several methods are known in the prior art for the preparation of this compound. For example, the so-called "direct method" proposed by E. G. Rochow is also applicable to the preparation of this silane compound in which metallic silicon and cyclopentyl chloride are reacted in the presence of a copper catalyst. Alternatively, it can be synthesized by the reaction of a cyclopentyl magnesium halide as a Grignard reagent with tetrachlorosilane.
The above mentioned "direct method" is not advantageous when the organosilane compound to be prepared is cyclopentyl trichlorosilane because by-products are formed in large amounts so that great difficulties are encountered in the isolation and purification of cyclopentyl trichlorosilane. The Grignard method has an economical disadvantage as an industrial method due to the expensiveness of the Grignard reagent in addition to the problem of troublesomeness and danger of fire or explosion accompanying the use of a very inflammable organic solvent such as ether. Moreover, the productivity of the Grignard method cannot be high enough due to the formation of a large amount of a magnesium halide as the by-product which must be removed from the reaction mixture. Further, the Grignard reagent, i.e. cyclopentyl magnesium halide, is highly susceptible to oxidation by oxygen in the atmospheric air to be converted into cyclopentyloxy magnesium halide from which cyclopentyloxy trichlorosilane is formed as the product of the Grignard reaction while this compound can hardly be separated from cyclopentyl trichlorosilane, for example, by distillation because these two compounds have physical properties very close to each other.
It would be a speculatively possible way that cyclopentyl trichlorosilane could be prepared by the hydrosilation reaction between trichlorosilane and cyclopentene in the presence of a platinum compound such as chloroplatinic acid as a catalyst according to a procedure well known in the hydrosilation between a silicon compound having a silicon-bonded hydrogen atom and a linear alkenyl compound. Different from other cycloalkene compounds such as cyclohexene of a 6-membered ring, nevertheless, no report is found in the literatures for the hydrosilation reaction of cyclopentene with trichlorosilane. This is presumably due to the low reactivity of cyclopentene even by the catalytic promotion of the reaction by conventional platinum catalysts.